JVM G1

2024-07-03

Enabling the G1 Garbage Collector in JVM

To enable the G1 (Garbage-First) Garbage Collector in the Java Virtual Machine (JVM), you need to specify the appropriate JVM options when starting your Java application. The G1 garbage collector is designed to provide high throughput and low latency, making it suitable for applications with large heaps.

Steps to Enable G1 Garbage Collector

  1. JVM Version: Ensure you're using a JVM version that supports G1. It's available in Java 7u4 and later versions.

  2. Command-Line Option: Use the -XX:+UseG1GC option to enable the G1 garbage collector. Here’s how you can specify it when starting your Java application:

    java -XX:+UseG1GC -jar your-application.jar

  3. Heap Size Specifications: You might want to specify initial and maximum heap sizes to optimize the G1 collector's performance. You can do this using -Xms for the initial heap size and -Xmx for the maximum heap size. For example:

    java -Xms512m -Xmx4g -XX:+UseG1GC -jar your-application.jar

  4. Tuning Parameters: G1 provides various tuning parameters for optimizing its performance. Some useful options include:

    • -XX:MaxGCPauseMillis=<n>: Set a target for the maximum garbage collection pause time (in milliseconds).
    • -XX:InitiatingHeapOccupancyPercent=<n>: Set the occupancy threshold (%) to start concurrent marking.
    • -XX:G1ReservePercent=<n>: Specify the percentage of the heap dedicated to a reserve that G1 can use.

  5. Monitoring and Logging: It’s helpful to enable verbose garbage collection logging to monitor the performance of the G1 collector. Use:

    -Xlog:gc*

Example Command

Here’s a practical example of starting a Java application with G1 enabled, specifying heap sizes, and logging options:

java -Xms512m -Xmx4g -XX:+UseG1GC -XX:MaxGCPauseMillis=200 -Xlog:gc* -jar your-application.jar

This command configures the G1 collector and helps you monitor its behavior during execution.